Hi tonynannini, my take is, greatly assisted by an online search not being very au fait with composer's construction methods.
The last piece being just that, his last composition and several "items" describe his method as "jigsaw construction" the following is an excerpt from one such item.
Elgar employed a highly personal mixture of these methods, which I became conversant with in my efforts to complete his Third Symphony, left only half finished at his death – methods, moreover, which were totally different from those which I employed in my own music. His procedure might be loosely compared to that of completing a jigsaw puzzle,